Systems and methods for reading rfid tags

ABSTRACT

An RFID system comprises an array of antennas each configured to emit a plurality of beams in different directions. The beams of each pair of adjacent antennas are directed towards one another and overlap. A pair of adjacent antennas transmits simultaneously and the overlapping beams interfere to create an interference pattern. An RFID reader controls the relative phase and/or frequency of the beams to move the interference pattern to read an RFID tag within the moving pattern. As the chance of a RFID tag responding to an emitted beam generally increases with signal strength of the reader beam an area of constructive interference means that RFID tags in that region are more likely to respond to the signal. The system can cover a large proportion of the area below ceiling-mounted antennas, where cover generally means that RFID tags in that area will be successfully read.

FIELD

This invention generally relates to reading passive radio frequency identification (RFID) tags, and in some implementations to a system comprising an array of antennas and one or more RFID readers.

BACKGROUND

The use of RFID methods for the identification of goods in both retail and industrial environments is well known. Each item of inventory is provided with a passive RFID tag. RFID readers, whose function is to register the tags and read associated information such as item description, are positioned to cover the area of interest. In environments having a very dense population of passive tags, for example large retail stores and industrial warehouses where tag densities may exceed 250 tags per square metre of floor area, current reader systems are able to register a typical maximum of 85% of the tags present in the area of interest. This represents a significant restriction to the usefulness of the system because a significant proportion of inventory is not registered.

Failure to register tags that are in the area intended to be covered by readers has two major causes: the failure of the reader antennas to illuminate the whole target area and interference to the process of reading the returns from scanned tags caused by collisions between tag responses or interference by further transmissions from other readers covering the same area.

We have previously described systems for reading passive radio frequency identification (RFID) tags in WO2011/135328 and WO2011/135329. Further background prior art can be found in US2010/0039231; US2013/0147609; and EP1544781A. However, there remains a need for improved techniques.

SUMMARY

The invention is defined in the claims.

According to a first aspect there is provided an RFID system for reading at least one RFID tag. The system may comprise an array of antennas, each antenna configured to emit a plurality of beams in different directions. The beams of each pair of adjacent antennas may be directed towards one another so that the beams overlap. The arrays may be ceiling-mounted. At least one RFID reader may be connected to at least two of the antennas such that at least one pair of adjacent antennas transmits simultaneously such that the overlapping beams interfere with one another to create an interference pattern. The at least one RFID reader may be configured to control at least one of the phase and the frequency of one of the interfering beams with respect to the other to move the interference pattern to read one or more RFID tags within the moving interference pattern.

Advantageously, the beams overlap at points in time to create a region of constructive interference. As the chance of a RFID tag responding to an emitted beam generally increases with signal strength of the emitted (reader) beam, the area of constructive interference means that RFID tags in that region are more likely to respond to the signal. The direction and phase of the beams can be controlled to direct regions of interferences toward an area containing RFID tags to be read. Therefore, embodiments can provide a system that can cover a large proportion of the area below the antennas, where cover generally means that RFID tags in that area will be successfully read.

In some prior art, interference between two readers (which may also function as transmitters) is avoided in all regions, however, implementations of the described system are configured to intentionally create regions of controlled interference between neighbouring antennas. In embodiments, the layout and geometry of the antennas of the array is such that these regions of controlled interference form a substantially continuous region of coverage.

In a preferred embodiment, each antenna is configured to emit n beams in n different radial directions. The array may be defined by nodes at which the antennas are located. The different directions may correspond to lines between nodes of the array.

Advantageously, this allows for different arrangements of antennas. Different implementations may have antennas emitting a different number of beams. For example, an arrangement where n=6 may result in a triangular grid, and an arrangement where n=3 may result in a hexagonal grid. The arrangement and geometry can be tailored, for example, to specific requirements of the desired coverage area, and/or to the shape, size and type of RFID tags likely to be within the area.

In some implementations each antenna comprises a set of antenna elements, and wherein the antenna has a corresponding set of connections, one for each beam direction, wherein the direction of a beam is dependent upon at least one of: a spacing between two antenna elements of said antenna an electronic configuration of said antenna; a shape of said antenna elements. The connections may be transmitting and/or receiving connections.

Advantageously, this allows for arrangements where the antennas are configured to optimally cover the area being targeted. Systems employing a single antenna emitting multiple beams facilitate providing coverage in multiple directions from the antenna and thus can minimize areas where there is low coverage.

Furthermore, by having each connection drive a beam in a given direction each beam direction can be adjusted independently rather than controlling all of the multiple beams emitted from an antenna in the same manner. Advantageously the approach further allows the possibility of having one port that is transmitting whilst another port receives a signal. Thus in implementations it is possible to transmit signals into one area of coverage and to receive signals from RFID tags in another direction.

Advantageously, implementations of the described system can also have multiple beams emitted at a given (simultaneous) time from a single antenna, rather than a reader triggering the beams to be emitted at separate times. This facilitates continuous coverage of an area associated with a given antenna.

In some implementations of the system the array of antennas defines multiple groups of antennas, where each group of antennas has an associated RFID reader, and where the RFID readers of the different groups operate at different frequencies. Adjacent groups may have at least one shared antenna and the system may be configured to control the RFID readers such that the shared antenna emits beams of two different frequencies in two different respective directions, one for each group.

In some implementations of the system the array of antennas extends over a region defining a pattern in which each group has a set of boundary antennas and a central antenna. Beams of the central antenna may be directed towards each boundary antenna; the boundary antennas may be shared between the groups.

Providing different groups of antennas operating at different frequencies helps to minimise unintentional interference between different groups of antennas. Although within a group there are regions of intentional interference, it may be disadvantageous to have inference between/across groups. Generally, the beams emitted from an antenna will point into and/or towards the group with which the beam is associated. Thus, in embodiments, each group may provide substantially continuous coverage within the group and minimal coverage outside of the group, minimising the effect of interference across groups. Furthermore, because multiple beams associated with multiple groups may be emitted from a single antenna the region of coverage generally covered by a group may border the coverage of the adjacent group. Therefore, by providing a system with multiple groups comprising antennas associated with multiple groups it is possible to have large continuous areas of coverage.

In embodiments, providing an antenna associated with different groups facilitates the groups to be more closely spaced together than if separate antennas were used for separate groups.

In some implementations of the system the RFID readers may be synchronized in frequency and/or transmit timing. For example in a wide area system there is a possibility that adjacent readers, even when on different frequencies, will cause reader-reader interference at the tag owing to the lack of frequency selectivity in low cost passive tags. Such interference may result in tags not being able to correctly demodulate reader commands. Synchronising the reader signal (modulation, and optionally protocol) across multiple readers e.g. such that they send substantially identical signals can suppress this problem. This can be achieved with synchronisation at the relatively low reader modulation rate, which is typically 100's kHz to 1 MHz.

Frequency synchronization may be used to inhibit adjacent readers from operating on the same frequency, which can cause interference at the reader's receiver from the adjacent reader transmitter if the modulation and protocol are not synchronised. This can arise from the signal (modulation) from one reader corrupting tag signals from another reader. Where the reader modulation and protocol are synchronised, it can be desirable to control the operating frequencies of adjacent readers such that their frequencies are well enough separated that the beat (difference) frequency is different, e.g. substantially different, from the modulation frequency.

In some implementations of the system the antennas are configured to be ceiling mounted. Each antenna may be configured to emit the plurality of beams in different lateral directions, each directed at an angle away from a plane defined by the array of antennas.

Advantageously, the lateral direction may provide overlapping regions of coverage with other antennas. The beams being directed away from the plane has an advantage that when the antennas are ceiling mounted the beam travels downwards in the direction of RFID tags positioned under the ceiling.

In some implementations of the system the RFID reader is configured to dither a relative phase of the overlapping beams.

The dithering of the relative phase can facilitate the creation of regions of constructive interference.

In some implementations of the system the RFID reader is configured to control a first antenna of the array to emit a first beam and a second beam. The first and second beams may differ in either time or frequency. The first beam may generates a first overlapping region with a beam emitted from a second antenna of the array and the second beam may generates a second overlapping region with a beam emitted from the second antenna. The first overlapping region may be on a first side of a dividing line joining the two antennas and the second overlapping region may be on a second side of the dividing line. This facilitates monitoring of a portal such as a door through which the RFID tags may pass.

In some implementations of the system the RFID system is further configured to count, for an identified tag, a number of tag reads or read rate on the first side of the line and on the second side of the line, and to determine, from a difference between the number of tag reads or read rate on each side of the line, probable movement of the identified tag towards, away or across the dividing line.

Transmission of the first and second beams may occur at different (non-overlapping) times; for example emission of the beams may alternate. This facilitates the system determining which beam emission triggered a given RFID tag to respond. Additionally or alternatively this advantage may also be provided by emitting beams of different frequencies. Creating overlapping regions of the beams advantageously provides for stronger signal coverage. Furthermore, two narrow overlapping beams can define a narrower area of coverage than a single beam of the same area. This may be used to more accurately determine the location of an RFID tag than may be possible with a single beam.

Embodiments could be installed over a doorway, which can define a boundary to be crossed. Embodiments can probabilistically determine whether an RFID tag is on one side of the doorway or another, and if the tag has moved from one side to another.

In some implementations of the system two or more antennas of the array of antennas define a dividing line. The RFID system may be configured to drive the antennas so that opposite sides of the dividing line are either i) alternately illuminated by the interfering beams or ii) illuminated by interfering beams of different frequencies. The RFID system may be configured to determine movement of a tag across the dividing line from respectively either i) a difference in read rate of the tag during the times of alternate illumination or ii) a difference in read rate of the tag at the different frequencies, as the tag moves from one side of the dividing line to the other.

According to a further aspect there is provided a method of reading at least one RFID tag. The method may comprise emitting from each antenna of an array of antennas a plurality of beams in different directions; the beams of each pair of adjacent antennas may be directed towards one another so that the beams overlap. The method may further comprise transmitting from at least one pair of adjacent antennas simultaneously such that the overlapping beams interfere with one another to create an interference pattern. The method may further comprise controlling at least one of the phase and the frequency of one of the interfering beams with respect to the other to move the interference pattern to read one or more RFID tags within the moving interference pattern.

In another aspect there is provided an RFID or radio system for reading one or more RFID tags or radio sensors. The system may comprise an antenna comprising an array of antenna elements. The system may further comprise a feed network configured to produce multiple discrete beams from the antenna elements, having multiple ports. Each port may be configured to produce a beam. The system may further comprise one or more RFID reader units or radio systems, each e.g. connected to a port of said feed network. The one or more RFID reader units or radio systems may be operated such that each beam of the antenna is simultaneously modulated with substantially different signals and/or has a different carrier frequency.

Some implementations of the above described, and other, RFID systems and methods may restrict the area of coverage of a particular antenna by transmitting a jamming signal from one or more other antennas such that the tags within the jamming area are unable to respond to the reader e.g. with an identifier such as an EPC (Electronic Product Code), even if sufficient field strength exists to activate the tag.

This can be advantageous where it is desired to create a sharp boundary between areas where tags are and are not read.

Thus there is also provided an RFID system or method as described above further comprising (use of) a system to transmit a jamming signal towards an area of tag-reading coverage of one or more of the antennas to define a boundary of the area of tag-reading coverage.

Thus there is also provided a method of reading at least one RFID tag, the method comprising: emitting a reading signal from at least one antenna, emitting a jamming signal from at least one (other) antenna, wherein the beams of the reading and jamming signals overlap to an extent to cause a sharp boundary between where tags are and are not able to be read. Here one or more of the antennas may be part of an antenna array.

Jamming can be achieved e.g. using a carrier modulated with frequency band limited noise or a pseudo random modulated signal similar to the reader to tag communication, or can be achieved by using signals which are compliant with the protocol, but purposefully inserting errors into acknowledgement packets. Due to the lack of frequency selectivity in RFID tags, jamming may occur on the same frequency as the RFID interrogator, or another channel within the band.

Thus in another aspect there is provided a method of reading at least one RFID tag, the method comprising: emitting a reading signal from at least one antenna, and emitting a jamming signal from at least one (other) antenna, wherein the beams of the reading and jamming signals overlap to an extent to cause a sharp boundary between where tags are and are not able to be read.

There is also provided an RFID system for reading at least one RFID tag, the system comprising: an RFID reader coupled to a first antenna for reading an RFID tag; and an RFID signal jammer coupled to a second antenna and configured to jam the RFID reader from reading the RFID tag.

The RFID signal jammer coupled to the second antenna may be configured to jam the RFID reader from reading the RFID tag when the RFID tag is beyond a tag reading boundary of the RFID reader, e.g. by directing the second antenna and/or adjusting a strength of the jamming signal.

The jamming may comprise transmitting noise and/or may comprise transmitting a signal according to a protocol of the RFID tag which includes an error check, wherein the jamming signal comprises data which is configured to fail the error check.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an RFID system 100 for reading at least one RFID tag.

FIG. 2 shows an RFID system 200.

FIG. 3a shows a group of antennas 300 with a central antenna configured to emit 6 beams in 6 different radial directions.

FIG. 3b shows a wide area array comprising groups of antennas as displayed in FIG. 3 a.

FIG. 4a shows a group of antennas with a central antenna configured to emit 3 beams in 3 different radial directions.

FIG. 4b shows a wide area array comprising groups of antennas as displayed in FIG. 4 a.

FIG. 5 shows an antenna 500 comprising multiple antennas elements 501, 503, 505, 507.

FIG. 6 shows an RFID system 600 comprising two adjacent groups of antennas (601, 603) having two shared antennas 605, 607.

FIG. 7 shows an RFID system comprising a group of antennas 700.

FIG. 8 shows multiple antennas 800 configured to be ceiling mounted.

FIG. 9 shows a RFID system 1000 comprising two antennas 1001, 1003 configured to generate an overlapping region (1005, 1007) on either side of a dividing line 1009.

FIG. 10 shows a schematic diagram 1100 displaying how the system 1000 is configured to determine movement of an identified tag 1101 towards, or away, or across the dividing line 1009.

FIG. 11 shows an embodiment of the system 1000 comprising two antennas configured to generate an overlapping region on either side of a dividing line at a first time ‘Period A’ 1201 and a second time ‘Period B’ 1203.

FIG. 12 shows an embodiment of the system 1000 comprising two antennas configured to configured to generate a first overlapping region 1301 on a first side of a dividing line at a first frequency f1, and a second overlapping region 1303 on a second side of a dividing line at a second frequency f2.

FIG. 13a shows an RFID system 1400 without a jammer antenna.

FIG. 13b shows an RFID system 1401 comprising a jammer antenna 1403.

FIG. 14 shows a schematic diagram of a method of jamming comprising transmitting noise and/or transmitting a signal according to a protocol of the RFID tag which includes an error check.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an RFID system 100 for reading at least one RFID tag. The RFID system 100 comprises an array of antennas 103, 105, 107, 109. Each of the antennas 103, 105, 107, 109 are configured to emit a plurality of beams in different directions. This is exemplified by the beams 111, 113, 115, 117 emitted by the antenna 103. The beams of each pair of adjacent antennas can be directed towards one another so that the beams overlap. This is shown in more detail in FIG. 2. The arrays may be ceiling-mounted, this is shown in more detail in FIG. 8. The RFID system 100 comprises a RFID reader 101 connected to each of the antennas 103, 105, 107, 109 via the connections 119, 121, 123, 125. The RFID reader 101 is configured to control at least one pair of adjacent antennas (e.g. 105 and 103) to transmit simultaneously such that the overlapping beams interfere with one another to create an interference pattern. The RFID reader 101 may be configured to control at least one of the phase and the frequency of one of the interfering beams with respect to the other to move the interference pattern to read one or more RFID tags within the moving interference pattern. As can be seen from the spacing 131, the spacing between antennas in an antenna array (e.g. antennas 109 and 107) is much larger than a wavelength of a beam emitted by an antenna.

FIG. 2 shows an RFID system 200. The RFID system 200 comprises two antennas, 203 and 205. The two antennas 205 and 203 are connected via connections 209 and 207 to a RFID reader 201. The RFID reader 201 is configured to control the phase and frequency of the beams emitted by antennas 205 and 203. The RFID system 200 is configured to create a region of interference 211. For example the region of interference 211 is created by a superposition of beam 213 (emitted by the antenna 205) and beam 215 (emitted by the antenna 203). Both constructive and destructive interference will occur at different locations within the region of interference 211. Adjusting the relative phase of the transmissions from antennas 213 and 215 will alter the locations of destructive and constructive interference. Adjusting e.g. the phase of each beam alters the inference pattern within the area of overlap to ‘dither’ the locations of the constructive and destructive interference, with the aim that over time all locations should achieve constructive interference. As the chance of a RFID tag responding to an emitted beam generally increases with signal strength of the emitted (reader) beam, the area of constructive interference 211 means that RFID tags in that region (i.e. region 211) are more likely to respond to the signal. The direction and phase of the beams (e.g. 213, 215) are controlled by the reader 201 to direct regions of interferences toward an area containing RFID tags to be read. Therefore, a system 200 can cover a large proportion of the area below the antennas 205 and 203.

The layout and geometry of the antennas 205 and 203 of the array is such that these regions of controlled interference 211 form a substantially continuous region of coverage.

FIG. 3a shows a group of antennas 300. Each antenna of the group of antennas 300 is configured to emit n beams in n different radial directions. The group of antennas 300 comprises a central antenna 301 configured to emit 6 beams (303, 305, 307, 309, 311, 313) in 6 different radial directions. The array (i.e. the group of antennas) 300 is defined by nodes at which the antennas are located. The different directions may correspond to lines between nodes of the array 300. This allows for different arrangements of antennas.

The group of antennas 300 is an embodiment where n=6 and forms a triangular grid 315. This can be seen in FIG. 3b which shows a wide area array 313 comprising groups of antennas as displayed in FIG. 3 a.

FIG. 4a shows a group of antennas 400 having a central antenna 401 configured to emit 3 beams in 3 different radial directions. For the group of antennas 400, n=3 and the antennas forms a hexagonal grid 403. The arrangement and geometry of the antennas 400 can be tailored, for example, to specific requirements of the desired coverage area, and/or to the shape, size and type of RFID tags likely to be within the area. FIG. 4b shows a wide area array 405 comprising groups of antennas as displayed in FIG. 4a . FIG. 4b displays the hexagonal arrangement 403.

FIG. 5 shows an antenna 500 comprising multiple antennas elements 501, 503, 505, 507. FIG. 5 shows a set of connections 509 corresponding to the antenna elements 501, 503, 505, 507 (one connection for each beam direction). The direction of a beam produced by one of the multiple antenna connections 509 is dependent upon at least one of: a spacing between two antenna elements of said antenna 500; an electronic configuration of said antenna 500 and feed network; a shape of said antenna elements 501, 503, 505, 507. The connections 509 are configured to be transmitting and/or receiving connections. This antenna 500 is configured to optimally cover the area being targeted. The single antenna 500 emits multiple beams and thus facilitate providing coverage in multiple directions from the antenna 500. This can reduce areas where there is low coverage.

In implementations each antenna connection passes signals to some or all of the antenna elements via the feed network. A configuration of the feed network may determine the phases and amplitudes of each element corresponding to a particular antenna connection, which together with the geometry and properties of the elements determines the beam direction and shape.

By having each connection of the group of connections 509 drive a beam in a given direction, each beam direction can be adjusted independently rather than controlling all of the multiple beams emitted from the antenna 500 in the same manner. Therefore the antenna 500 is configured to allow one port that is transmitting whilst another port receives a signal. Thus antenna 500 is configured to transmit signals into one area of coverage and to receive signals from RFID tags in another direction.

The antenna 500 is also configured to emit multiple beams at a given (simultaneous) time, rather than a reader (not shown) triggering the beams of antenna 500 to be emitted at separate times. This facilitates continuous coverage of an area associated with the antenna 500.

As can be seen by the spacing 513, the spacing between antenna elements in an antenna is approximately equal to a wavelength of the beam emitted by the antenna element.

FIG. 6 shows an RFID system 600 comprising two adjacent groups of antennas (601, 603) having two shared antennas 605, 607. Each group of antennas 601, 603 has an associated RFID reader 609, 611 respectively. The RFID reader 609 operates at a different frequency to the RFID reader 611. The adjacent groups 601, 603 comprise two shared antennas (605, 607). The system 600 is configured to control the RFID readers 609, 611 such that a shared antenna emits beams of two different frequencies in two different respective directions, one for each group. For example, FIG. 6 shows the RFID reader 609 controlling the shared antenna 607 to emit a beam 613 at a first frequency in the direction of the antenna group 601. For example, FIG. 6 further shows the RFID reader 611 controlling the shared antenna 607 to emit a beam 615 at a second frequency in the direction of the antenna group 603.

FIG. 7 shows an RFID system comprising a group of antennas 700. The group of antennas comprises multiple boundary antennas (701, 703, 705, 707, 709, 711) and a central antenna 713. The possible beams (e.g. 715) of the central antenna 713 are directed towards each boundary antenna. One or more of the boundary antennas (701, 703, 705, 707, 709, 711) may be shared between the further groups of antennas. The group of antennas 700 are configured to operate at a different frequency to an adjacent group. This helps to reduce unintentional interference between different groups of antennas. Although within the group 700 there are regions of intentional interference (not shown), it may be disadvantageous to have inference between/across groups. The beams emitted from the antennas of the group 700 will point into and/or towards the group with which the beam is associated. Thus, the group 700 can provide substantially continuous coverage within the group 700 and minimal coverage outside of the group. This minimising the effect of interference across groups. Furthermore, and in reference to FIG. 6, because multiple beams associated with multiple groups are emitted from a single antenna (see beams 613, 615 emitted from antenna 607), the region of coverage generally covered by the group 601 borders the coverage of the adjacent group 603. Therefore, a system with multiple groups comprising antennas associated with multiple groups (such as system 600), it is possible to have large continuous areas of coverage.

Further referring to FIG. 6, because the antenna 607 is associated with group 601 and group 603, the groups 601 and 603 can be more closely spaced together than if separate antennas were used for the separate groups 601 and 603.

In the system 600, the RFID readers are synchronized in frequency and/or transmit timing. In the system 600 there is a possibility that adjacent readers 609 and 611, even when operating on different frequencies, will cause reader-reader interference at the tag owing to the lack of frequency selectivity in low cost passive tags. Such interference may result in tags not being able to correctly demodulate reader commands. Therefore the system 600 is configured to synchronise the reader signal (modulation, and optionally protocol) across readers 609 and 611 to suppress this problem. This can be achieved with synchronisation at the relatively low reader modulation rate, which is typically 100's kHz to 1 MHz.

In system 600, frequency synchronization is used to inhibit adjacent readers 609 and 611 from operating on the same frequency, which can cause interference at the reader's receiver from the adjacent reader transmitter if the modulation and protocol are not synchronised. This can arise from the signal (modulation) from one reader corrupting tag signals from another reader. System 600 is further configured to control the operating frequencies of the adjacent readers 609 and 611 such that their frequencies are well enough separated that the beat (difference) frequency is different, e.g. substantially different, from the modulation frequency. In an alternative arrangement, readers 609, 611 may use a listen before for talk (LBT) scheme to avoid selecting the same channel.

FIG. 8 shows multiple antennas 800 configured to be ceiling mounted. Each antenna (801, 803, 805, 807) is configured to emit a plurality of beams in different lateral directions, each directed at an angle away from a plane defined by the array of antennas. For example, FIG. 8 shows that antenna (801) is configured to emit a beam 809 in a lateral direction. The beam 809 is directed at an angle 813 away from a plane defined by the array of antennas. The component of the projection of the beam in a direction on to the plane is shown by the line 815, whilst the component of the projection of the beam in a direction normal to the plane is shown by line 817. The lateral direction 811 provides overlapping regions of coverage with other antennas (e.g. between antennas 801 and 807). The beam 809 being directed away from (i.e. normal to the plane, i.e. in direction 817) the plane has an advantage that when the antennas (801, 803, 805, 807) are ceiling mounted, the beams travel downwards (i.e. in the direction of 817) in the direction of RFID tags positioned under the ceiling.

In some implementations of the system, the RFID reader is configured to dither a relative phase of the overlapping beams. The dithering of the relative phase can facilitate the creation of regions of constructive interference.

FIG. 9 shows a RFID system 1000 comprising two antennas 1001, 1003 configured to generate an overlapping region (1005, 1007) on either side of a dividing line 1009. In the system 1000, a RFID reader (not shown) is configured to control a first antenna 1001 of the array to emit a first beam 1011 and a second beam 1013. The first beam 1011 and second beam 1013 differ in either time or frequency. The first beam 1011 and second beam 1013 differing in time is discussed with reference to FIG. 11 whilst the first beam 1011 and second beam 1013 differing in frequency is discussed with reference to FIG. 12. With reference to FIG. 9, the first beam 1011 generates a first overlapping region 1005 with a beam 1015 emitted from the second antenna 1003 of the array. The second beam 1013 generates a second overlapping region 1007 with a beam 1017 emitted from the second antenna 1003. The first overlapping region 1005 is on a first side 1019 of the dividing line 1009 joining the two antennas 1001 and 1003. The second overlapping region 1007 is on a second side 1023 of the dividing line 1009. This facilitates monitoring of a portal such as a door through which the RFID tags may pass.

FIG. 10 shows a schematic diagram 1100 displaying how the system 1000 is configured to determine movement of an identified tag 1101 towards, or away, or across the dividing line 1009. Time is represented by the horizontal arrow 1103. The RFID system 1000 is further configured to count over a sliding time interval, for an identified tag 1101, a number of tag reads, and/or read rate, on the first side of the line 1019 and on the second side of the line 1023, and to determine, from a difference between the number of tag reads or read rate on each side of the line, probable movement of the identified tag towards, away or across the dividing line.

FIG. 11 shows an embodiment of the system 1000 comprising two antennas configured to generate an overlapping region on either side of a dividing line at a first time ‘Period A’ 1201 and a second time ‘Period B’ 1203. In the system 1000 shown in FIG. 11, a transmission of the first beam 1011 and second beam 1013 occurs at different (non-overlapping) times 1201 and 1203. In other words, the emission of the beams 1011 and 1013 from the antenna 1001, alternates. This facilitates the system 1000 determining which beam emission triggered a given RFID tag to respond. This advantage may also be provided by the antenna 1001 emitting beams 1011 and 1013 having different frequencies. Creating overlapping regions of the beams advantageously provides for stronger signal coverage. Furthermore, two narrow overlapping beams (such as beams 1011 and 1015) define a narrower area of coverage than a single beam of the same area. This is used in the system 1000 to more accurately determine the location of an RFID tag than may be possible with a single beam.

FIG. 12 shows an embodiment of the system 1000 comprising two antennas configured to configured to generate a first overlapping region 1301 on a first side of a dividing line at a first frequency f1, and a second overlapping region 1303 on a second side of a dividing line at a second frequency f2.

The embodiments of FIG. 11 and FIG. 12 may be alternatives. The embodiments of FIG. 11 and FIG. 12 may be combined so as to produce two overlapping regions, each region on either side of a dividing line, where the two overlapping regions differ in frequency and differ in time.

Embodiments of the system 1000 can be installed over a doorway, which can define a boundary to be crossed. Embodiments of the system 1000 can probabilistically determine whether an RFID tag is on one side of the doorway or another, and if the tag has moved from one side to another.

As described, the system 1000 comprises two antennas of an array of antennas that define a dividing line 1009. The RFID system 1000 may be configured to drive the antennas so that opposite sides of the dividing line are either i) alternately illuminated by the interfering beams as displayed in FIG. 11 or ii) illuminated by interfering beams of different frequencies as displayed in FIG. 12. The RFID system 1000 is configured to determine movement of a tag across the dividing line from respectively either i) a difference in read rate of the tag during the times of alternate illumination or ii) a difference in read rate of the tag at the different frequencies, as the tag moves from one side of the dividing line to the other.

In an example use a plurality of beams is emitted from each antenna of an array of antennas as previously described, in different directions. The beams of each pair of adjacent antennas are directed towards one another so that the beams overlap. An interference pattern is created using overlapping beams by transmitting from one or more pairs of adjacent antennas simultaneously. The phase and/or frequency of one of the interfering beams is varied with respect to the other to move the interference pattern, and the RFID tag(s) are read within the moving interference pattern.

There is further described an RFID or radio system for reading one or more RFID tags or radio sensors. The system comprises an antenna comprising an array of antenna elements. The system may comprises a feed network configured to produce multiple discrete beams from the antenna elements, having multiple ports. Each port may be configured to produce a beam. The system comprises one or more RFID reader units or radio systems, each e.g. connected to a port of said feed network. The one or more RFID reader units or radio systems are operated such that each beam of the antenna is simultaneously modulated with substantially different signals and/or has a different carrier frequency.

FIG. 13a shows an RFID system 1400 without a jammer antenna. FIG. 13b shows an RFID system 1401 comprising a jammer antenna 1403. The RFID system 1401 can restrict the area of coverage of a particular antenna (e.g. antennas 1403, 1405) by transmitting a jamming signal from jamming antenna 1403 such that the tags within the jamming area 1405 are unable to respond to the reader with an identifier such as an EPC (Electronic Product Code), even if sufficient field strength exists to activate the tag. This is advantageous where it is desired to create a sharp boundary (e.g. ‘better defined read boundary’ 1407) between areas where tags are and are not read. The system 1400 is thus configured to transmit a jamming signal towards an area of tag-reading coverage of one or more of the antennas 1405, 1403 to define a boundary of the area of tag-reading coverage.

FIG. 14 shows a schematic diagram of a method of jamming comprising transmitting noise and/or transmitting a signal according to a protocol of the RFID tag which includes an error check, wherein the jamming signal comprises data which is configured to fail the error check. Such a method may comprise of emitting a jamming signal comprising data which is configured to fail an error check. The jamming may comprise transmitting noise and/or may comprise transmitting a signal according to a protocol of the RFID tag which includes an error check, wherein the jamming signal comprises data which is configured to fail the error check.

In FIG. 14, the horizontal arrow 1501 represents time. At a first time a reader and a jammer transmit a same, well-formed query command 1503. At a later time, a tag response to the queries with a random 16 bit handle (RN16) 1505. Following this, the reader responds with an acknowledgement 1507 containing the same RN16 that was emitted by the tag, the jammer responds with an acknowledgment 1509 that is known to be an incorrect RN16. Therefore, the tag never transmits an EPC (96 bit identifier). Jamming can be achieved e.g. using a carrier modulated with frequency band limited noise or a pseudo random modulated signal similar to the reader to tag communication, or can be achieved by using signals which are compliant with the protocol, but purposefully inserting errors into acknowledgement packets.

Thus a method of reading an RFID tag may comprise emitting a reading signal from a first antenna and emitting a jamming signal from a second, jammer antenna. In some implementations the beams of the reading and jamming signals are arranged to overlap sufficiently to cause a sharp boundary between where tags are and are not able to be read. One or more of the antennas may be part of an antenna array.

A RFID system for performing the method e.g. of FIG. 14 comprises: an RFID reader coupled to a first antenna for reading an RFID tag; and an RFID signal jammer coupled to a second antenna and configured to jam the RFID reader from reading the RFID tag. The RFID signal jammer coupled to the second antenna may be configured to jam the RFID reader from reading the RFID tag when the RFID tag is beyond a tag reading boundary of the RFID reader, e.g. by directing the second antenna and/or adjusting a strength of the jamming signal.

Many alternatives will occur to the skilled person. The invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto. 

1. An RFID system for reading at least one RFID tag, the system comprising: an array of antennas, each antenna is configured to emit a plurality of beams in different directions, wherein the beams of each pair of adjacent antennas are directed towards one another so that the beams overlap, at least one RFID reader connected to at least two of the antennas such that at least one pair of adjacent antennas transmits simultaneously such that the overlapping beams interfere with one another to create an interference pattern, wherein the at least one RFID reader is configured to control at least one of the phase and the frequency of one of the interfering beams with respect to the other to move the interference pattern to read one or more RFID tags within the moving interference pattern.
 2. The system of claim 1 wherein each antenna is configured to emit n beams in n different radial directions, wherein the array is defined by nodes at which the antennas are located, and wherein the different directions correspond to lines between nodes of the array.
 3. The system of claim 1 wherein each antenna comprises a set of antenna elements, and wherein the antenna has a corresponding set of connections, one for each beam direction.
 4. The system of claim 1, the array of antennas defines multiple groups of antennas, wherein each group of antennas has an associated RFID reader, and wherein the RFID readers of the different groups operate at different frequencies, wherein adjacent groups have at least one shared antenna, and the system is configured to control the RFID readers such that the shared antenna is configured to emit beams of two different frequencies in two different respective directions, one for each group.
 5. The system of claim 4 wherein the array of antennas extends over a region defining a pattern in which each group has a set of boundary antennas and a central antenna, wherein beams of the central antenna point towards each boundary antenna, and wherein the boundary antennas are shared between the groups.
 6. The system of claim 4 wherein the RFID readers are synchronized in frequency and/or transmit timing.
 7. The system of 1, wherein the antennas are configured to be ceiling mounted, and wherein each antenna is configured to emit the plurality of beams in different lateral directions and are directed away from a plane defined by the array of antennas.
 8. The system of claim 1, wherein the RFID reader is configured to dither a relative phase of the overlapping beams.
 9. The system of claim 1, wherein: the RFID reader is configured to control a first antenna of the array to emit a first beam and a second beam, wherein the first and second beams differ in either time or frequency; and wherein the first beam generates a first overlapping region with a beam emitted from a second antenna of the array and the second beam generates a second overlapping region with a beam emitted from the second antenna; and wherein the first overlapping region is on a first side of a dividing line joining the two antennas and the second overlapping region is on a second side of the dividing line.
 10. The system of claim 9 wherein the RFID system is configured to count, for an identified tag, a number of tag reads or read rate on the first side of the line and on the second side of the line, and to determine, from a difference between the number of tag reads or read rate on each side of the line, probable movement of the identified tag towards, away or across the dividing line.
 11. An RFID system as claimed in claim 1, wherein two or more antennas of the array of antennas defines a dividing line, wherein the RFID system is configured to drive the antennas so that opposite sides of the dividing line are either i) alternately illuminated by the interfering beams or ii) illuminated by interfering beams of different frequencies, and wherein the RFID system is configured to determine movement of a tag across the dividing line from respectively either i) a difference in read rate of the tag during the times of alternate illumination or ii) a difference in read rate of the tag at the different frequencies, as the tag moves from one side of the dividing line to the other.
 12. A method of reading at least one RFID tag, the method comprising: emitting from each antenna of an array of antennas a plurality of beams in different directions, wherein the beams of each pair of adjacent antennas are directed towards one another so that the beams overlap, transmitting from at least one pair of adjacent antennas simultaneously such that the overlapping beams interfere with one another to create an interference pattern, controlling at least one of the phase and the frequency of one of the interfering beams with respect to the other to move the interference pattern to read one or more RFID tags within the moving interference pattern.
 13. An RFID or radio system for reading one or more RFID tags or radio sensors, the system comprising: an antenna comprising an array of antenna elements; a feed network configured to produce multiple discrete beams from the antenna elements, having multiple ports, wherein each port is configured to produce a beam; and one or more RFID reader units or radio systems, each connected to a port of said feed network; and wherein the one or more RFID reader units or radio systems are operated such that each beam of the antenna is simultaneously modulated with substantially different signals and/or has a different carrier frequency.
 14. An RFID system or method as recited in claim 1, further comprising a system to transmit a jamming signal towards an area of tag-reading coverage of one or more of the antennas to define a boundary of the area of tag-reading coverage.
 15. A method of reading at least one RFID tag, the method comprising: emitting a reading signal from at least one antenna, emitting a jamming signal from at least one other antenna, wherein the beams of the reading and jamming signals overlap to an extent to cause a sharp boundary between where tags are and are not able to be read.
 16. An RFID system for reading at least one RFID tag, the system comprising: an RFID reader coupled to a first antenna for reading an RFID tag; and an RFID signal jammer coupled to a second antenna and configured to jam the RFID reader from reading the RFID tag.
 17. An RFID system as claimed in claim 16 wherein the RFID signal jammer coupled to the second antenna is configured to jam the RFID reader from reading the RFID tag when the RFID tag is beyond a tag reading boundary of the RFID reader.
 18. An RFID system or method as claimed in claim 15, wherein the jamming comprises transmitting noise.
 19. An RFID system or method as claimed in claim 15, wherein the jamming comprises transmitting a signal according to a protocol of the RFID tag which includes an error check, and wherein the jamming signal comprises data which is configured to fail the error check. 